This kind of clamping apparatuses is described in Japanese Patent Public Disclosure No. 10-277858, for example.
This prior art is composed so that, during a locking operation, a compression spring composed of a plurality of coned disc springs moves a plurality of balls from a disengaging position to an engaging position, and then the compression spring axially drives an insertion pin via the balls, which are in the engaging position, for locking.
By the way, an urging force of the compression spring is maximized in a fully compressed state, and decreases as the spring expands.
Therefore, in the prior art, the urging force of the compression spring decreases according to an idling stroke for moving the balls from the disengaging positions to the engaging positions. As a result, the urging force for the locking operation decreases, resulting in a small locking force. The larger the idling stroke of the clamping apparatus is, the more conspicuous this problem grows.
It is an object of the present invention to provide a spring-type clamping apparatus having a strong locking force.